The present invention relates generally to energy management, and more particularly to electrical energy load shifting in order to reduce energy costs. More particularly, the invention concerns systems and methods that permit electrical energy to be purchased and stored during off-peak hours, and the stored energy to be used and/or sold back to the power grid during peak hours, to thereby realize savings in energy costs.
Energy demand at a premises typically varies over the time of day. In a typical home, there is a peak in the morning when the family gets up, turns on lights, radios and televisions, cooks breakfast, and heats hot water to make up for the amount used in showers. When the family leaves for work and school, it may leave the clothes washer and dishwasher running, but when these are done, demand drops to a lower level, but not to zero, as the air conditioners, refrigerators, hot water heaters and the like continue to operate. Usage goes up as the family returns, peaking around dinner when the entire family is home. This creates the typical “double hump” demand curve as shown in FIG. 1. Therein, it is seen that there is a morning peak 1 and an evening peak 3 of electrical energy demand.
Businesses tend to follow different patterns depending on the nature of the business. For example, usage is typically low when the building is closed, and may be relatively constant when the office building is open. In extreme climates where air conditioning cannot be cut back overnight, energy use over the course of the day is more constant. Businesses like restaurants may start later in morning and their peak may extend further into the evening. A factory with an energy intensive process operating three shifts may show little or variation over the course of the day.
The incremental cost to a utility company for generating or purchasing electrical energy increases dramatically during periods of peak use over periods of off-peak usage. Using such information, electrical utility companies will often employ time of day-based rate schedule to charge a significantly higher rate for electrical energy (e.g., cost per kilowatt-hour) consumed during peak usage hours, as compared to energy consumed during off-peak hours, in order to compensate for its higher costs. For example, homes and small businesses may pay for electricity on a per-kilowatt hour basis with one rate applying during off-peak hours, and another, higher, rate applying during peak hours. The higher rates charged during peak usage periods can lead to significantly higher energy costs for the consumer, especially when the consumer's period(s) of high demand coincides with or falls within the interval set by the utility as peak hours.
The irregular curve in the graph of FIG. 2 plots a hypothetical price of electricity to a consumer (in cents/kWh) from the grid over the course of a day. As is common in many areas, this price varies significantly. The time of day rates are designed to reflect the marginally higher cost of power production at the peak demand periods of morning and early evening. At these times, utilities must dispatch power from their least efficient units, while, when cost is lower, they need provide power only from the most efficient units. In this rate diagram, there is a broad morning peak rate period 5, a “shoulder” rate period (also commonly referred to as a “partial peak” or “interim peak” period) in the early evening, and a peak rate period 9 in an evening period following the shoulder rate period. Remaining are off-peak rate periods 11.
Electric utilities have on occasion arranged to install special devices in homes and businesses that, when remotely activated by the utility, cut power to certain devices (e.g., air conditioners or hot water heaters) during peak loading conditions. Customers who agree to install such devices are given discounts or other incentives for installing such devices, and in exchange the utility is able to better manage energy demand remotely. However, such arrangements are made for the benefit of the utility, whose interests may be at odds with the interests and energy requirements of the consumer.
Recently, devices have been developed that help users reduce the cost of electricity purchases from the power grid by storing electricity in batteries, which are then drawn down during peak hours to reduce demand from the grid. The batteries can be charged during non-peak hours, thus reducing the total cost of electricity, and electricity can be sold back to the grid during favorable conditions. Some of these devices can produce energy from secondary sources such as solar panels, fuel cells, and other sources. Such devices, e.g., as described in U.S. patent application Ser. No. 11/144,834, filed on Jun. 6, 2005 (entitled “Optimized Energy Management System”), can also reschedule deferrable electrical consumption to off-peak hours. For example, a dishwasher can be automatically scheduled to turn on during off-peak hours.
It would be desirable to help energy consumers better manage the use of electrical energy storage devices, e.g., batteries, for more effectively shifting the consumption of electrical energy from peak to off-peak hours, to thereby reduce overall electrical energy consumption costs. Apparatus, systems and methods in accordance with the present invention provide significant advancements in this regard.